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Water Deliveries to Users Delivery of water to different users are affected dramatically by different scenarios, depending on streamflow changes and the application of the law of the river. For example, in the base case, deliveries to the Central Arizona Project would ordinarily fall to their minimum level 20 percent of the time and scheduled deliveries are met or exceeded 40 percent of the time. If runoff drops 5 percent, our results suggest that full scheduled deliveries will be met in only 25 percent of the years and that in half of the years, only minimum levels are delivered. Although the delivery data suggest that Mexico is affected only in extreme cases, the quality of Mexican water decreases significantly. In fact, all Lower Basin users would suffer a significant decline in water quality (see Salinity), Hvdroelectrlcltv Under current operating rules. hydroelectricity production, like reservoir storage, Is extremely sensitive to changes In runoff. If flows In the Upper Basin were to decrease by 10 percent, average annual storage decreases by 30 percent and power production drops by 26 percent. A decrease In flows of 20 percent would reduce storage by 63 percent and power production by nearly 50 percent. An Increase In flows of 10 percent would Increase storage by 28 percent and power generation by 21 percent. In the Lower Basin, a 10 percent decrease In runoff reduces storage by 30 percent and power production by 36 percent. A drop In runoff of 20 percent reduces Lower Basin storage by 50 percent and power production by 65 percent. Sallnltv The most critical concern for the Lower Basin Is salinity and salinity Is the only water-quality parameter studied. Even In the baSe-case scenario salinity criteria are consistently exceeded at all points In the Lower Basin for most years. Decreases In runoff of only 5 percent cause salinity criteria to be exceeded In virtually all years. Even If average flows were to Increase by 20 percent, salinity criteria are exceeded continuously for long periods. Under almost no climate-change circumstances can existing water-quality criteria be met given projected demands and operating constraints. Our results suggest that at least a 20 percent Increase In natural runoff would be necessary to bring the salinity levels In the Lower Basin Into compliance with existing criteria, In the absence of other activities to reduce salinity In the river. Seasonal Tlmlna of Runoff A variety of recent hydrologic analyses have suggested that changes In the seasonality of runoff may xII